Human auditory perception takes place primarily through the ears, but it is supported by the sense of touch especially at lower end of frequency spectrum. As an example, at frequencies below 50 Hz, sound pressure levels above 80 dB are typically required in order to make a sound perceivable by a human listener. At such sound pressure levels, human skin starts to vibrate at perceivable levels as well, resulting in the sense of touch, i.e. the vibrotactile sense, that server to support hearing. At frequencies below 20 Hz (infrasonic frequencies), hearing or sensing of air pressure vibrations is solely based on vibrotactile perception. In addition to very low frequencies below 20 Hz, the frequency range of vibrotactile perception on skin typically extends up to approximately 500 Hz, while for sensitized people who may have sensory impairments with other senses it may extend even up to approximately 1000 Hz. Thus, the vibrotactile sense, i.e. the sense of touch, supports human hearing in a considerable part of the perceivable audio frequency spectrum.
In parallel, active noise cancellation (ANC) technology for attenuating or even completely eliminating unwanted sounds within limited volumes are known in the art. Perhaps the most well-known application of ANC involves noise-cancelling headphones, where a microphone arrangement that serves to capture ambient noise around a user of the headphones is installed in the headphones, where an ANC processing unit generates ‘anti-noise’ that, when output to the user of the headphones, results in significantly attenuating or even completely eliminating the ambient noise captured by the microphone arrangement.
Quite obviously, such an ANC application is only capable of attenuating or eliminating audible perception of ambient noise, whereas the vibrotactile perception remains uncompensated for.